1. Field of the Invention
The present invention relates to a semiconductor thin film formed on a substrate having an insulative surface and a semiconductor device using such a semiconductor thin film as its active layer. In particular, the invention relates to such a semiconductor thin film and semiconductor device in which the semiconductor thin film is made of a material having silicon as the main component.
In this specification, the term "semiconductor device" is used as including all of devices that function by utilizing a semiconductor, and specifically includes the following.
(1) Single elements such as a thin-film transistor PA1 (2) Semiconductor circuits using a single element of item (1) PA1 (3) Electro-optical devices using a single element of item (1) or a semiconductor circuit of item (2) PA1 (4) Electronic devices using a semiconductor circuit of item (2) or an electro-optical device of item (3) PA1 (1) At least the channel forming region is constituted of a semiconductor thin film that is a collected body of a plurality of rod-like or flat-rod-like crystals, the surface orientation of the semiconductor thin film is approximately equal to {110} orientation, and almost all of crystal lattices of the semiconductor thin film have continuity at any crystal boundary. PA1 (2) At least the channel forming region is constituted of a semiconductor thin film that is a collected body of a plurality of rod-like or flat-rod-like crystals, the surface orientation of the semiconductor thin film is approximately equal to {110} orientation, and almost all of lattice fringes of the semiconductor thin film that are detected so as to traverse any grain boundary of different crystal grains extend straight and are continuous there.
2. Description of the Related Art
In recent years, the techniques of forming thin-film transistors (TFTs) by using a semiconductor thin film (thickness: hundreds to thousands of angstrom) formed on a substrate having an insulative surface have attracted much attention. Thin-film transistors are commonly used in various electronic devices such as ICs and electro-optical devices, and are now being developed at high speed particularly as switching elements of an image display device.
For example, in liquid crystal display devices, it is attempted to apply TFTs to every kind of electric circuit such as a pixel matrix circuit in which pixel regions arranged in matrix form are controlled individually, a driver circuit for controlling the pixel matrix circuit, or a logic circuit (a processor circuit, a memory circuit, or the like) for processing an external data signal.
At present, TFTs using an amorphous silicon film as an active layer have been put into practical use. However, TFTs using a crystal silicon film such as a polysilicon film are necessary for electric circuits, such as a driver circuit and a logic circuit, that are required to operate at even higher speed.
For example, techniques of the present assignee that are disclosed in Japanese Unexamined Patent Publication Nos. 7-130652 and 8-78329 are known as methods for forming a crystalline silicon film on a glass substrate. The disclosure of these publications is incorporated herein by reference. By utilizing a catalyst element for accelerating crystallization of an amorphous silicon film, the techniques of these publications enable formation of a crystal silicon film having superior crystallinity by a heat treatment of 500-600.degree. C. and about 4 hours.
In particular, the technique of the publication No. 8-78329 is such that the above technique is utilized to cause crystal growth in a direction approximately parallel with the substrate surface. The present inventors especially call a resulting crystallized region a "lateral growth region."
However, even a driver circuit that is constructed by using such TFTs cannot completely provide required performance. In particular, at present, it is impossible to construct, by using conventional TFTs, high-speed logic circuits that are required to operate at extremely high speed (megahertz to gigahertz).
To improve the crystallinity of a crystalline silicon film having grain boundaries (called a polycrystalline silicon film), the inventors have repeated trial and error as exemplified by a semi-amorphous semiconductor (Japanese Unexamined Patent Publication No. 57-160121 etc.) and a monodomain semiconductor (Japanese Unexamined Patent Publication No. 8-139019).
The concept common to the semiconductor films described in the above publications is to make grain boundaries substantially harmless. That is, the most important object was to substantially eliminate grain boundaries to thereby enable smooth movement of carriers (electrons or holes).
However, the semiconductor films described in the above publications are still insufficient to allow logic circuits to perform required high-speed operation. That is, to realize a system-on-panel incorporating logic circuits, it is necessary to develop a material that is not known, i.e., an entirely new material.